Method of tanning hides and skins



Patented Oct. 16, 1934 METHOD OF TANNING-RIDES AND SKINS Kenneth E.Bell, Marblehead, and Milton 0. McDonald, Salem, Mass., assigiiors to A.C. Lawrence Leather Company, Boston, Mass, a

corporation of Maine No Drawing. Application March 29, 1933, Serial No.663,374

8 Claims. (01. 149-5) The present invention relates to the method oftanning hides and skins.

In the usual method of tanning with compounds of chromium or chrometanning as it is usually called, the hides or skins are previouslytreated for the removal of hair and prepared for the tanning operationby pickling in an acid and salt solution.

The actual tanning is usually done by drume W ming the pickled skins ina solution of basic chromium sulfate until the skin is thoroughlyimpregnated. After this, the addition of sodium bicarbonate solutionserves to neutralize the acid present in the skins and allowsthe basic Mchromium compound thus present to react with the hide fibres, to tanthem.

In such a process the hide decreases in area and fat wrinkles tend tobecome exaggerated. The present invention provides a method of chrometanning that will overcome these difficulties and give not. only auniformly smooth surface, but an even greater area than that of theoriginal hide, at the same time reducing thetime required.

These objects are accomplished, generally speaking, by extending theuntanned skins to remove all wrinkles and folds and to stretch theskins, and holding them so extended while the fibres are being set bythe tanning action.

Preferably, the skins will be pickled in the usual manner and drummedwith the basic chrome sulfate solution until the latter has penetratedthroughout the body of the skin.

a The skins are then removed from the wheel and slicked onto a platewith the grain face of the skin in contact with the surface of theplate.

This slicking process serves not only to remove any wrinkles or creasesand to extend the skin to or even beyond its original size, but removesto more or less of the surplus watery content of the skin.

To the flesh side of the skins thus slicked out upon the plate isapplied the alkaline solution in any suitable manner and amount.

The skins may be left upon the plate until the tanning'process has beencompleted, or if desired, they may be removed after the tanning hasproceeded sufiiicientlyfar to set the skin or hide in its flat andextended condition, and the tanning completed off the plate without anysubstantial change in the shape or area of the hide.

As an example of one. way of practising the improved method of tanning,the skins which have been pickled with the salt and sulphuric acidsolution are placed in a wheel or drum with enough water so that theskins may be able to move and slip freely over one another and theinterior of the drum, and with suflicient common salt to repress theswelling of the skins. To thedrum is now added through the hollow shaftor gudgeon a solution equal to seven or eight per cent. of the weight ofthe drained pickled stock. The basis of this solution is basic chromiumsulfate CR(OH')SO4 and is commonly mixed in the proportions of 1.8 to2.5 pounds of the basic chromium sulfate per gallon of water.

A common and convenient method of preparing this solution is by the useof tanolin-R, so called, a satisfactory solution being secured by mixingthree and one-half to five pounds of 'tanolin per gallon of water,giving a basicity in the neighborhood of 34, which facilitates andhastens the penetration and distribution of this solution into andthrough the hide substance.

The tanning solution is added over a period of one-half hour, duringwhich time the wheel is in continuous motion and the skins are beingdrummed. This is for the purpose of uniformly distributing the tanningsolution throughout so the hide substance preparatory to the actualtanning thereof.

The wheel is now stopped and the skins, which are still soft, flexible,and extensible, are removed and are slicked, grain side down, onto 8 a'fibre board or other smooth surface plate. This slicking operationsmooths out and stretches the skins, the degree or amount of stretchbeingcontrolled to a considerable extentby the operator. Where themaximum 0 footage is desired, the operator will work the skin out to thegreatest area, reducing the thickness in so doing. If, on the otherhand, a maximum footage is' not desired, but rather uniformity ofthickness, the operator will endeavor 5 g to work down the thicker partsof the skin to the same thickness as the originally thinner parts.

This slicking operation also removes a great deal of the watery contentof the skin which would tend to dilute and retard the action of thealkaline solution.

With the skin slicked out and extended upon the plate, a solution of asecond tanning agent, viz. sodium bicarbonate, is applied to the fleshor exposed side, to render the tanning solution effective to fix orprecipitate chrome 'on or in the fibres and thus to tan the skin. Thissolution is preferably of A to of 1% strength and is applied with a swabor sponge, usually three applications being made at intervals ofone-half hour. Preferably the skin will be left on the plate for a shorttime after the last application inorder to secure the best results, butif desired, it may be removed after the first application withsatisfactory results, as the setting of the skin or hide occursprincipally in the earlier portions of the tanning operation.

Due to the fact that the skins so slicked out and extended have theirentire surface ex ed to the second solution, a much quicker tanning'action is secured than where, as previously was wise exposed to theaction of'the alkaline solulimited to the use. of the specific reagentshereinbefore described, as in its broader aspects it contemplates theuse of two or more reagents applied successively to the skin to set thefibres and effect the tanning thereof, while the latter is extended insmooth condition without wrinkles or creases, or is even stretchedbeyond its original size.

Having thus described the invention, what is claimed is:

L'That improvement in the method of tanning hides and skins whichcomprises subjecting 'is maintained in such extended condition withsodium bicarbonate to effect the tanning of the hide or skin.

2. That improvement in methods of tanning hides and skins whichcomprises subjecting the hide or skin to treatment by a tanning agent inthe presence of a material for rendering such' $1011 or a o i thereof,and then immediately'\ agent ineffective and until such agent has fullyslicked before the tanning has had time to proceed suflici'ently to setor fix the hide.

Instead of swabbing the alkaline solution upon the exposed face oftheskin it may be sprayed on it or flushed or flowed onto the hide while itis being slicked or' squeegeed, thus causing a sort of pumping action totake place in and between the fibres of the skin, and thus speeding upthe absorption of the tanningmaterial and hastening thetanning'operation.

Where the skins are removed from the boards before the completion of,the tanning operation, but after the hide has been sufficiently set topermit such removal, the tamiing may be com-.

pleted by drumming the skins in the wheel with the alkaline solution.

. If" desired, instead of applying the basic chromium-sulfate to thehide by drumming, 'as above described, the pickled skin may be slickeddirectly onto the plate and the basic chromium sulfate applied to theexposed surface of the skin as by swabbing or spraying, the applicationbeing repeated until theliquor has penetrated throughout the body of theskin after which the alkaline solutionis applied.

In order to hasten the action of the reagents and the tanning of thehide, the tanning process may be carried out at temperaturesconsiderably above the ordinary room temperature, but below those atwhich the hide would dry and shrink or "curl excessively. To avoid suchdrying at elevated temperatures, a relatively high humidity may bemaintained. Satisfactory results have been secured by retaining :thehides between successive applications of the tanning solution in closedchambers at temperatures of 120 with 100% relative humidity.

may be applied to the plate if desired. Splits will ordinarily beslicked with the split face against the plate, although not necessarilyso.

While the tanning reagents will ordinarily be applied in the form ofsolutions, they are not necessarily so applied but may be used in solidor semi-solid form insofar as their action permits.

* -Nor is the present invention necessarily penetrated the hideor skin,then before tanning has taken place slicking out the hide or skin upon asupporting surface, and treating the hide or skin while it is maintainedon such surface with a substance to render said material inefiectiveinorder to permit the tanning agent -to effect tanning of the hide orskin.

3. That improvement in methods of tanning hides and skins whichcomprises subjecting the hide or skin to treatment in solution of atanning agent in the presence of a retarding material for retarding theaction of such agent und until the hide or skin has been fully permeatedwith such tanning agent, then, before tanning has 3 taken place,slicking the hide or skin out upon a supporting surface and renderingthe retarding material ineffective in order to permit the tanning agentto efiect tanning of the hide or skin.

4. That improvement in methods of tanning hides and skins whichcomprises subjecting the hide or skin to treatment by a tanning agentduration of time sumcient, but for the acid condition of the skin, toefiect tanning thereof, and until such agent has fully permeated thehide or skin, thenstretching the untanned hide or skin upon a supportingsurface, and applying to the hide or skin an alkaline solution tocounteract the acid condition and cause tanning of the hide or skinwhile the latter i'smaintained.

on said supporting surface.

6. That improvementpin methods of tanning hides and skins whichcomprises drumming the hides or skins in mass in a solution of chromiumsalt in the presence of an acid, stretching each untanned hide or skinin extended condition and simultaneously therewith removing a largeproportion of the watery content "of each hide or skin, and applying tothe hide or skin an alkaline solution in a qpantity suflicient to causethe chromium salt to combine with the fibres of the hide or skin to setor tan the latter while it is maintained in its extended condition.

7. That improvement in methods of tanning hides and skins whichcomprises subjecting the hide or skin to treatment by a taming agent inthe presence of a material for rendering such agent inefiective,stretching the untamed hide or skin, and while maintaining such hide orskin in extended condition rendering said tanning agent eflective tocause tanning action 0 the hide or skin.

8. That improvement in methods of tanning hides and skins whichcomprises subjecting the hide or skin to treatment by a tanning agent inthe presence of an acid, then before tanning has taken place, stretchingthe hide or skin and thereafter rendering the hide or skin less acid tocause the tanning agent to eflect tanning thereof.

KENNETH E. BELL.

MHJTON C. MCDONALD.

